Case Study of Safety, Security and Safeguards (3S) Interfaces for a Very High Temperature Reactor System - 2025

The Generation IV International Forum (GIF) was established as a co-operative international endeavour aimed at developing the research necessary to evaluate the feasibility and performance of fourth generation nuclear systems (Gen-IV systems), with the objective of making them available for industrial deployment by 2030. 

The potential conflicts and synergies at the interfaces between the regimes of safety, security, and safeguards (2S and 3S interfaces) in nuclear facilities are increasingly apparent. With Gen-IV systems seeking to move towards deployment, it is an opportune moment to further develop guidance on how to effectively identify and address these 2S and 3S interfaces during the earliest design stages. 

To this end, the GIF Proliferation Resistance & Physical Protection Working Group (PRPPWG), the GIF Risk & Safety Working Group (RSWG) and the GIF Very High Temperature Reactor System Steering Committee (VHTR-SSC) conducted a bottom-up 3S interface case study exercise on a notional pebble bed VHTR modular reactor. The objective of this exercise was to identify and characterize the 2S and 3S interfaces on the reference system, thereby developing some technology-neutral guidelines for the identification and characterization of 2S and 3S interfaces. This report presents a summary of the outcomes of this work. 

The primary objective of the bottom-up case study is to offer some guidance to designers and vendors interested in implementing a 3S-by-design (3SBD) approach to the development of a Gen-IV advanced modular reactor. The 3S interfaces can be analysed pairwise (3 x 2S), or in an integrated fashion at the simultaneous intersection of all three regimes (3S). Although the concept of 3SBD is not novel, there is a need among designers to foster both security and safeguards by design to integrate with the already existing safety by design culture. An intermediate analysis of the existing interfaces using a 3 x 2S framework can facilitate the realization of 3SBD culture among designers more effectively and expeditiously. Consequently, the case study considers both 2S and 3S interfaces. Among the most critical aspects of the interfaces considered are those that would compromise the objectives of each S regime, potentially leading to conflicts between each regime. This typically arises from the sharing of space, time, or resources between the regimes. Equally, analysing how each interface shares space, time, or resources can either mitigate these conflicts or bring positive synergistic outcomes. The optimized sharing of space, time and resources holds special relevance for small or advanced modular reactors that occupy smaller spaces and/or utilize fewer resources compared to traditional large nuclear installations. These critical aspects distilled from the case study, are summarized in this report. 

Those interested in a “quick-start guide” to this case study can jump to the tables provided in Section 8.2 which summarize the critical aspects of the interfaces identified in the case study; the sections in Chapter 7. provide in-depth explanation of these interfaces. Further, more general characteristics of the interfaces are found in Section 8.3 that provide principles for identifying interfaces in a nuclear facility. It has been observed that many of the interfaces identified in this report, except for a security-safeguards interface particular to the fuel pebble handling system, possess generic characteristics that can be readily applied to other Gen-IV energy systems. Although this study is not completely comprehensive in coverage of all 3S interfaces of a pebble bed VHTR reactor system, many of the critical aspects of the 3S interfaces identified should be easily generalizable to other reactor types